Robert Biegler

BLOCKING IN THE SPATIAL DOMAIN WITH ARRAYS OF DISCRETE LANDMARKS

A characteristic feature of associative conditioning is that learning a predictive relationship between two events can block later learning about an added event. It is not yet well established whether blocking occurs in the spatial domain or the circumstances in which it does. We now report, using rats trained to search for hidden food near landmarks in an open field arena, that blocking can occur in spatial learning. The animals noticed the added landmark at the start of the blocking phase and explored it, but either failed to incorporate it into their spatial map or developed a representation in which only some landmarks actually control behavior. Additionally, performance at asymptote was controlled by the shape of the landmark array rather than the individual landmarks comprising it, indicating that blocking in the spatial domain may represent a failure to alter the encoded geometry of a learned array.

Landmark Stability: Further Studies Pointing to a Role in Spatial Learning

Two experiments were conducted to investigate the possible role of landmark stability in spatial learning. Rats were trained to search in a large arena for food hidden at a consistent distance and direction from either a single radially symmetric landmark or an array of two landmarks. We varied the relative degree to which the landmark array and/or the cues of the training context predicted the location of food, without varying the conditional probability of food being available given either cue. Experiment 1 used vestibular disorientation to ensure control of search location by experimenter-controlled cues. The results showed that making either a single landmark or a cluster of two adjacent landmarks the sole spatial predictor of reward location reduced the accuracy of search compared to a condition where both the landmark array and context cues were reliable spatial predictors. Varying global landmark stability had no effect when training was conducted using an array of two landmarks located some distance from each other. Context cues, when tested alone, triggered very little searching in appropriate locations, and the absolute magnitude of control over search was insufficient to account for the superiority of stable landmarks. The better learning with a stable landmark, and the dependence of this effect on the geometrical arrangement of landmarks, points to the conditions of spatial learning involving additional principles to those of simple associative conditioning. Experiment 2 examined landmark stability using a single landmark and fixed directional cues in the absence of vestibular disorientation. This also revealed a relative advantage of landmark stability, but animals with a landmark that moved from trial to trial did show some evidence of learning. Context cues when tested alone had minimal influence. Parametric manipulation of landmark stability offers a novel way of influencing spatial learning and thus understanding better the process through which egocentric representations of perceived space are transformed into allocentric representations of the real world. The purpose of this paper is to describe two experiments concerned with identifying the psychological processes of allocentric spatial learning. The results point to the idea that landmark stability is an important factor in spatial learning. Specifically, they reveal that whether or not a landmark will be used for the purpose of representing the location of another object (including hidden objects) is influenced by whether it is perceived as geometrically stable with respect to at least one other landmark and/or certain geometric features of the environment. This phenomenon is relevant to the application of associative learning principles to the spatial domain.

Possible uses of path integration in animal navigation

Path integration, in its simplest form, keeps track of movement from a starting point and so makes it possible to return to this point. Path integration can also be used to build a metric spatial representation of the environment, if given a suitable readout mechanism that can store and recall the coordinates of any one of multiple locations. A simple averaging process can make this representation as accurate as desired, given enough visits to the locations stored in the representation. There are more than these two ways of using path integration in navigation. They can be classified systematically according to the following three criteria: Is there one point at which coordinates can be reset to correct errors, or several? Is there one possible goal, or several? Is there one path integrator, or several? I describe the resulting eight methods of using path integration and compare their characteristics with the available experimental evidence. The classification offers a theoretical framework for further research.

Precision and Reliability in Animal Navigation

Uncertainty plays an important role in several navigational computations. Navigation typically depends on multiple sources of information, and different navigational systems may operate both in parallel and in combination. The optimal combination of information from different sources must take into account the uncertainty of that information. We distinguish between two types of spatial uncertainty, precision, and reliability. Precision is the inverse variance of the probability distribution that describes the information a cue contributes to an organism’s knowledge of its location. Reliability is the probability of the cue being correctly identified, or the probability of a cue being related to a target location. We argue that in most environments, precision and reliability are negatively correlated. In case of cue conflict, precision and reliability must be traded off against each other. We offer a quantitative description of optimal behaviour. Knowledge of uncertainty is also needed to optimally determine the point where a search should start when an organism has more precise spatial information in one of the spatial dimensions. We show that if there is any cost to travel, it is advantageous to head off to one side of the most likely target location and head toward the target. The magnitude of the optimal offset depends on both travel cost and search cost.

Ordinality and novel sequence learning in jackdaws.

A hallmark of higher cognition is the flexible use of information. This requires an abstract representation of the information. In sequence learning, ordinal position knowledge is seen as a more versatile representation when compared to chaining. Here, we assessed which of these mental representations is the most natural and most dominant in jackdaws. Two jackdaws (Corvus monedula) were trained on 14 separate three-item sequences (triplets), made up of abstract images. On each trial, the three items of one triplet were presented in fixed order. The images represented either the first, second or third ordinal position. Test stimuli consisted of the three images and a distractor image that was chosen randomly from the remaining sequences. We rewarded pecking in the correct order to the images belonging to the same sequence. The most common error the birds made was to peck at a distractor item from the same ordinal position. To look at how versatile the jackdaws’ ordinal knowledge was, we replaced a familiar item with a novel item in some sequences. We then created novel sequences with these items, which the birds completed correctly. It appears, then, that jackdaws have a concept of ordinal position.

Optimal cache search depends on precision of spatial memory and pilfering, but what if that knowledge is not perfect?

The problem of when an action should be abandoned because it is not worth further effort occurs in many situations. In the spatial domain, the relevant information can be quantified. Two essential pieces of information are the precision with which the target location and the probability of the target being present are known. We offer a quantitative description of optimal solutions to cache retrieval, treating it as a 2D investment problem with search cost proportional to area. We estimated the value of knowing the precision of spatial information and the precision of information regarding probability: how precisely should you estimate the precision of your knowledge? We compared the expected gain from assessing the precision of spatial knowledge and probability with the expected gain from decisions based on aggregate knowledge of the distribution of precision and probability. We found that heuristics, represented here as default search limits based on aggregate knowledge, are useful only under limited conditions.

Insufficient evidence for habituation in Mimosa pudica . Response to Gagliano et al. (2014)

Gagliano et al. (Oecologia 175(1):63–72, 2014) reported that Mimosa pudica habituates to repeated stimulation, as shown by a reduction in response, dishabituation, and stimulus specificity. I argue that Gagliano et al.’s data show an absence of dishabituation, that their experimental design needs an additional condition to test whether there is stimulus specificity, and that most of their data can be explained by motor fatigue. Some data are not easily explained by fatigue, and I suggest a further analysis that may clarify the issue. The status of habituation in Mimosa remains uncertain.

Identifying the Computational Parameters Gone Awry in Psychosis

Probabilistic inference is assumed to be aberrant in deluded patients. Here, we present two novel tasks, designed to measure these computational parameters. Our shape precision task measures the precision of visual short term memory and perceived precision (confidence judgement). This provides a direct assessment of the prediction error. Our probability task is a modification of the “beads in a jar” task. Our version asks for probability estimates after each bead drawn. We derived the mathematical optimal solution and compared it to the estimates of the participants. 15 healthy subjects and 15 patients diagnosed with psychosis played the tasks. Results: patients think their memory is better than it actually is. Further, their probability judgment is worse than that of healthy controls. There was a strong correlation between perceived precision and the probability judgements. Thus, both tasks may measure the same underlying statistical inference mechanism – which is disturbed in deluded patients.

Do adjustments in search behavior depend on the precision of spatial memory

Various forms of uncertainty are important for decision making. How aware are we of the precision of knowledge, and how accessible it is? In three experiments, an assessment of the precision of spatial memory was needed to make optimal decisions. First, we examined search strategies in a search task in which the most efficient strategy was to head to one side of the target by a margin depending on the precision of spatial information, the “where to start” task. We found that nine out of of our 20 human subjects adapted the margin according to precision. Second, we let the subjects search for the location of a sample picture. On one-third of the trials, the target was not present, making it a “when to stop searching” task. We found that the subjects did not adjust their investment in search according to their precision. In the third experiment, we looked at whether there was transfer between the two tasks. Subjects who had been reminded of the relevance of uncertainty by the “where to start” task increased their search effort more in the “when to stop searching” task. Thus, the results show that the use of information about precision is not automatic, but can be triggered.